本文主要是以背向階梯流場中的下游發展現象與演化過程作為研究目標，探討一階梯高為10mm，其突張比為1.13的標準背向階梯結構中，固定入口自由流平均速度為15.09m/s，藉由以不同的初始進口條件改變實驗的控制參數Reθ，來觀察其對下游流場的發展現象之影響。
本研究係以Reθ為878及1053兩不同的初始進口條件，以紊流強度及雷諾剪應力來觀察下游流場的邊界層與自由流間的分布外，也加入了三階紊流參數(Turbulent triple-product)來探討階梯下游流場的相關紊流特性，同時也比較了下游流場不同截面的偏態係數(Skewness)與峰態係數(Kurtosis)的分布。而由實驗結果得知，在背向階梯下游流場的發展現象中，不論是代表速度擾動值的紊流強度或是動量傳遞大小的雷諾應力，其演化的過程均是隨著流場往下游的發展而呈現消退且擴散的趨勢，係符合了紊流能量傳遞的瀑流原理(energy cascade theory)。
此外，由於邊界層內的流體動量均是往自由流區傳遞，故在自由流與邊界層的交界面有著間歇性的渦流傳遞現象存在，而此交界處產生的間歇性渦流流逸(intermittent bursts)便造成了速度分布的偏斜現象，而偏態及峰態係數在統計學上便是用來分析資料偏斜與離散程度的因子，在相較於以平均速度分布來判定邊界層厚度而言，此間歇性的渦流流逸其所能造成平均值上的影響是有限的，故以偏態係數及峰態係數來判定再成長邊界層的分布，則是較符合流體現象上的物理意義。而由實驗結果觀察到，Reθ值的大小對於背向階梯下游流場之再成長邊界層的發展過程則是有顯著的影響。

The purpose of this thesis is to experimentally explore the downstream development of backward-facing step flow with the configuration of 10 mm in step’s height and 1.13 in the aspect ratio under two different Reynolds numbers of Reθ = 878 and 1053.
The inlet mean velocity is fixed at 15.09 m/s but the inlet Reynolds numbers based on the momentum boundary thickness, Reθ, are changed by means of controlling the inlet momentum boundary layer thickness .
Evolution of the sectional files of turbulent proportions including turbulent intensities, Reynolds stress, some turbulent triple-products, skewness coefficient and kurtosis coefficient are presented under the two different conditions of Reθ = 878 and 1053. It is found that the turbulent intensities and Reynolds stress are decayed and diffused from the boundary layer to the free stream region along the flow direction. The evolution tendency is consistent with the turbulent energy cascade theory.
There exist the intermittent burst in the interface between the boundary layer and the free stream region, which leads to the skewness of the instantaneous velocity distributions. It is more physically meaningful in estimating the redeveloped boundary layer thickness on the bases of the peak values of the skewness coefficient and the kurtosis coefficient than on the basis of the mean streamwise velocity distribution. It is found that the Reθ value has significant effect on the development of the redeveloped boundary layer.

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